1. Field of the Invention
The present application relates to a system for controlling gene expression of gene products that affect cell fate determination in mammalian cells in response to an endogenous or exogenous ligand.
2. Background
The control of expression of genes introduced into mammalian cells is of great interest for a variety of applications including gene therapy and cellular immunotherapeutics.
Cellular immunotherapeutics is an active area of research seeking to harness and improve the capabilities of the immune system to combat various diseases, most prominently cancer. Research in the last decade has demonstrated that the natural immune system is central to the defense against tumorigenic malignancies in immunocompetent individuals (Blattman, J. N. & Greenberg, P. D. Cancer immunotherapy: a treatment for the masses. Science 305, 200-205 (2004); Shankaran, V. et al. IFNgamma and lymphocytes prevent primary tumour development and shape tumour immunogenicity. Nature 410, 1107-1111 (2001)). T cells with both natural and synthetic receptors for tumor-associated antigens have been shown to have tumor specific targeting and cytolytic activities (Morgan, R. A. et al. Cancer regression in patients after transfer of genetically engineered lymphocytes. Science 314, 126-129 (2006); Robbins, P. F. et al. Cutting edge: persistence of transferred lymphocyte clonotypes correlates with cancer regression in patients receiving cell transfer therapy. J. Immunol. 173, 7125-7130 (2004); Leen, A. M., Rooney, C. M. & Foster, A. E. Improving T cell therapy for cancer. Annu Rev Immunol 25, 243-265 (2007)). Compared to conventional cancer treatments such as radiation and chemotherapy, cellular immunotherapeutics significantly reduces off-target effects and the associated non-specific toxicity to healthy tissues. The promise of a new treatment paradigm with improved safety and efficacy has driven the development of various cellular immunotherapeutic strategies.
As an example, the adoptive transfer of antigen-specific T cells can reconstitute immunity to viruses and virus-induced malignancy and be therapeutically effective in humans (Riddell, S. R. et al. Restoration of viral immunity in immunodeficient humans by the adoptive transfer of T cell clones. Science 257, 238-241 (1992); Comoli, P. et al. T cell therapy of Epstein-Barr virus and adenovirus infections after hemopoietic stem cell transplant. Blood Cells Mol Dis 40, 68-70 (2008); June, C. H. Principles of adoptive T cell cancer therapy. J Clin Invest 117, 1204-1212 (2007)). The identification of tumor antigens and improvements in gene transfer methodology has made it feasible to isolate tumor-reactive T cells or to engineer T cells to express receptors that target transformed cells (Rosenberg, S. A. et al. Gene transfer into humans—immunotherapy of patients with advanced melanoma, using tumor-infiltrating lymphocytes modified by retroviral gene transduction. N Engl J Med 323, 570-578 (1990); Kahlon, K. S. et al. Specific recognition and killing of glioblastoma multiforme by interleukin 13-zetakine redirected cytolytic T cells. Cancer Res 64, 9160-9166 (2004)). Regression of advanced tumors has been observed in a subset of melanoma patients treated with T cells specific for melanocyte differentiation antigens (Morgan (2006); Huang, J. et al. Survival, persistence, and progressive differentiation of adoptively transferred tumor-reactive T cells associated with tumor regression. J Immunother (1997) 28, 258-267 (2005)), but therapy often fails or induces only a temporary response. Limitations in T-cell therapy include the inability of transferred tumor-specific T cells to persist in the tumor-bearing host (Rosenberg (1990); Dudley, M. E. et al. Adoptive transfer of cloned melanoma-reactive T lymphocytes for the treatment of patients with metastatic melanoma. J Immunother 24, 363-373 (2001); Yee, C. et al. Adoptive T cell therapy using antigen-specific CD8+ T cell clones for the treatment of patients with metastatic melanoma: in vivo persistence, migration, and antitumor effect of transferred T cells. Proc Natl Acad Sci USA 99, 16168-16173 (2002); Mackensen, A. et al. Phase I study of adoptive T-cell therapy using antigen-specific CD8+ T cells for the treatment of patients with metastatic melanoma. J Clin Oncol 24, 5060-5069 (2006).). Therefore, genetic systems that allow for tight, tunable, and regulatable control over the proliferation and activation of T cells are critical to the practical application of therapies based on engineering of immune system function.